Carbon Nanotubes-Based Label-Free Affinity Sensors for Environmental Monitoring

Nanostructures, such as nanowires, nanobelts, nanosprings, and nanotubes, are receiving growing interest as transducer elements of bio/chemical sensors as they provide high sensitivity, multiplexing, small size, and portability. Single-walled carbon nanotubes (SWNTs) are one such class of nanostructure materials that exhibit superior sensing behavior due to its large-surface carbon atoms that are highly responsive to surface adsorption events. Further, their compatibility with modern microfabrication technologies and facile functionalization with molecular recognition elements make them promising candidates for bio/chemical sensors applications. Here, we review recent results on nanosensors based on SWNTs modified with biological receptors such as aptamers, antibodies, and binding proteins, to develop highly sensitive, selective, rapid, and cost-effective label-free chemiresistor/field-effect transistor nanobiosensors for applications in environmental monitoring.     

Label-free electrical detection of pyrophosphate generated from DNA polymerase reactions on field-effect devices

We introduce a label-free approach for sensing polymerase reactions on deoxyribonucleic acid (DNA) using a chelator-modified silicon-on-insulator field-effect transistor (SOI-FET) that exhibits selective and reversible electrical response to pyrophosphate anions. The chemical modification of the sensor surface was designed to include rolling-circle amplification (RCA) DNA colonies for locally enhanced pyrophosphate (PPi) signal generation and sensors with immobilized chelators for capture and surface-sensitive detection of diffusible reaction by-products. While detecting arrays of enzymatic base incorporation reactions is typically accomplished using optical fluorescence or chemiluminescence techniques, our results suggest that it is possible to develop scalable and portable PPi-specific sensors and platforms for broad biomedical applications such as DNA sequencing and microbe detection using surface-sensitive electrical readout techniques.     

核酸适体功能化的二维材料场效应晶体管传感器研究进展

二维材料场效应晶体管传感器具有可调的电学性质和高的灵敏度, 非常适合用于构建高性能的传感器, 应用于疾病诊断和环境监测等领域. 核酸适体是一种生物识别分子, 具有特异性强、 稳定性高等优势. 近年来, 核酸适体功能化的二维材料场效应晶体管传感器在医疗诊断和环境监测等领域取得了显著的研究进展. 本文综合评述了核酸适体功能化的二维材料场效应晶体管传感器的最新研究进展, 对场效应晶体管传感器的结构及传感原理进行了概括, 详细介绍了二维材料的制备方法以及核酸适体功能化器件的设计原理. 在此基础上, 对核酸适体功能化的二维材料场效应晶体管传感器在疾病诊断和环境监测领域的应用进展进行了概述, 讨论了核酸适体功能化的二维材料场效应晶体管传感器面临的一些问题和挑战, 对其发展前景进行了展望.     

Development of a new matrix based on a silicone ladder polymer for ion-sensing membranes.

A silicone ladder-type polymer was successfully utilized for a matrix of an ion sensing membrane to fabricate an ion-sensitive field-effect transistor. An ion sensing membrane was readily fabricated by mixing a silicone ladder-type oligomer with a quaternary ammonium salt, casting onto the gate of the field-effect transistor, and polymerizing with heating. Since no acid catalysts were needed to prepare the ion sensing membrane, it was possible to keep the quaternary ammonium salt in the matrix without decomposition. The ion-sensitive field-effect transistor based on the silicone ladder-type polymer and the quaternary ammonium salt showed a linear response with a slope of -58.1 mV decade(-1) very close to the theoretical Nernstian response over an NO3- range between 3.0 x 10(-6) and 1.0 x 10(-1) M. The time required to reach 90% total response was within 5 s, when the NO3- concentration was changed from 1.0 x 10(-3) to 3.0 x 10(-3) M. The newly fabricated ion-sensitive field-effect transistors have kept their original sensitivity for more than half a year.     

Surface immobilizable chelator for label-free electrical detection of pyrophosphate

A new pyrophosphate (PPi) chelator was designed for surface-sensitive electrical detection of biomolecular reactions. This article describes the synthesis of the PPi-selective receptor, its surface immobilization and application to label-free electrical detection on a silicon-based field-effect transistor (FET) sensor.     

电位无标型糖化血红蛋白免疫微传感器

研制了基于标准CMOS工艺和微加工技术的电位无标型免疫微传感器,可实现糖化血红蛋白浓度与血红蛋白浓度的简便检测。该微传感器包括含有信号读出电路的场效应型微传感集成芯片和一次性测试试条。微传感集成芯片由本实验室设计并经新加坡Chartered半导体公司流片制备。一次性测试试条采用微加工技术制备于柔性塑料片上,包括敏感电极阵列和三维微结构测量池。基于自组装单层膜并引入纳米金颗粒的方法,在测试试条电极表面固定抗体。采用循环伏安法和交流阻抗法对电极表面的修饰过程进行了测试和分析。该传感器对糖化血红蛋白和血红蛋白检测的线性范围分别为4～24mg/L和60～180mg/L。     

Effect of morphology on organic thin film transistor sensors

This review provides a general introduction to organic field-effect transistors and their application as chemical sensors. Thin film transistor device performance is greatly affected by the molecular structure and morphology of the organic semiconductor layer. Various methods for organic semiconductor deposition are surveyed. Recent progress in the fabrication of organic thin film transistor sensors as well as the correlation between morphology and analyte response is discussed.     

Transistor-Based Work-Function Measurement of Metal–Organic Frameworks for Ultra-Low-Power,Rationally Designed Chemical Sensors

A classic challenge in chemical sensing is selectivity. Metal–organic frameworks (MOFs) are an exciting class of materials because they can be tuned for selective chemical adsorption. Adsorption events trigger work-function shifts, which can be detected with a chemical-sensitive field-effect transistor (power ≈microwatts). In this work, several case studies were used towards generalizing the sensing mechanism, ultimately towards our metal-centric hypothesis. HKUST-1 was used as a proof-of-principle humidity sensor. The response is thickness independent, meaning the response is surface localized. ZIF-8 is demonstrated to be an NO₂-sensing material, and the response is dominated by adsorption at metal sites. Finally, MFM-300(In) shows how standard hard–soft acid–base theory can be used to qualitatively predict sensor responses. This paper sets the groundwork for using the tunability of metal–organic frameworks for chemical sensing with distributed, scalable devices.     

Label-free biosensors based on aptamer-modified graphene field-effect transistors

A label-free immunosensor based on an aptamer-modified graphene field-effect transistor (G-FET) is demonstrated. Immunoglobulin E (IgE) aptamers with an approximate height of 3 nm were successfully immobilized on a graphene surface, as confirmed by atomic force microscopy. The aptamer-modified G-FET showed selective electrical detection of IgE protein. From the dependence of the drain current variation on the IgE concentration, the dissociation constant was estimated to be 47 nM, indicating good affinity and the potential for G-FETs to be used in biological sensors.     

Electronic aptamer-based sensors

The selection of aptamers-nucleic acids that specifically bind low-molecular-weight substrates or proteins-by the SELEX (systematic evolution of ligands by exponential enrichment) procedure has attracted recent efforts directed to the development of new specific recognition units. In particular, extensive activities have been directed to the application of aptamers as versatile materials for the design of biosensors. The Minireview summarizes the recent accomplishments in developing electronic aptamer-based sensors (aptasensors), which include electrochemical, field-effect transistor, and microgravimetric quartz crystal microbalance sensors, and describes methods to develop amplified aptasensor devices and label-free aptasensors.     

Integrated microelectronic device for label-free nucleic acid amplification and detection

We present an integrated microelectronic device for amplification and label-free detection of nucleic acids. Amplification by polymerase chain reaction (PCR) is achieved with on-chip metal resistive heaters, temperature sensors, and microfluidic valves. We demonstrate a rapid thermocycling with rates of up to 50 degrees C s(-1) and a PCR product yield equivalent to that of a bench-top system. Amplicons within the PCR product are detected by their intrinsic charge with a silicon field-effect sensor. Similar to existing optical approaches with intercalators such as SYBR Green, our sensing approach can directly detect standard double-stranded PCR product, while in contrast, our sensor does not require labeling reagents. By combining amplification and detection on the same device, we show that the presence or absence of a particular DNA sequence can be determined by converting the analog surface potential output of the field-effect sensor to a simple digital true/false readout.     

Chemically-modified nanopores for sensing

Sensing with chemically-modified nanopores is an emerging field that is expected to have major impact on bioanalysis and fundamental understanding of nanoscale chemical interactions down to the single-molecule level. The main strength of nanopore sensing is that it implies the prospect of label-free single-molecule detection by taking advantage of the built-in transport-modulation-based amplification mechanism. At present, fabrication and application of solid-state nanopores are becoming the focus of attention because, compared with their biological counterparts, they offer greater flexibility in terms of shape, size, and surface properties, as well as superior robustness. A breakthrough in label-free nanopore sensing for real-world applications is therefore expected from implementing solid-state nanopores, an area that is still developing. Without claiming comprehensiveness, the focus of this review comprises recent results and trends in nanopore-based sensing (i.e. emerging technologies for fabricating solid-state nanopores, their chemical functionalization, and detection methods for quantitative analysis).     

Organic semiconductors in potentiometric gas sensors

Solid-state potentiometric sensors based on the chemical modulation of the work function of organic semiconductors are discussed. The theory of the chemical work function modulation is briefly reviewed. There are several sensor configurations, in which this transduction principle can be employed. First is the Kelvin probe, second is the chemically sensitive field-effect transistor in which the conventional metal gate of the silicon-based transistor has been replaced by an organic semiconductor. Chemical modulation of work function enters also into the operation of the third type of sensor discussed in this review, on “organic field-effect transistor”. It is shown that in reality such sensors are “field-modulated chemiresistors”, rather than potentiometric sensors.     

Phthalocyanines as Sensitive Materials for Chemical Sensors

This paper provides a review of phthalocyan- ines suitable for the development of chemical sensors. Phthalocyanines may be utilized for different types of chemical sensors, including in particular electronic conductance sensors [such as semiconductive, field-effect transistor (FET), solid-state ionic and capacitance sensors], mass-sensitive sensors utilizing a quartz crystal microbalance (QCM) and surface acoustic-wave (SAW) sensors, and optical sensors. The phthalocyanines used are discussed in terms of their physical and chemical properties, as well as their sensitivity, selectivity and reversibility towards the detection of NO₂ and organic solvent vapours. The interaction mechanism between phthalocyanine films and analyte molecules is also discussed.     

Inkjet printed (bio)chemical sensing devices

Inkjet printing has evolved from an office printing application to become an important tool in industrial mass fabrication. In parallel, this technology is increasingly used in research laboratories around the world for the fabrication of entire (bio)chemical sensing devices or single functional elements of such devices. Regularly stated characteristics of inkjet printing making it attractive to replace an alternative material deposition method are low cost, simplicity, high resolution, speed, reproducibility, flexibility, non-contact, and low amount of waste generated. With this review, we give an overview over areas of (bio)chemical sensing device development profiting from inkjet printing applications. A variety of printable functional sensor elements are introduced by examples, and the advantages and challenges of the inkjet method are pointed out. It is demonstrated that inkjet printing is already a routine tool for the fabrication of some (bio)chemical sensing devices, but also that novel applications are being continuously developed. Finally, some inherent limitations of the method and challenges for the further exploitation of this technology are pointed out.     

Field-effect transistor chemical sensors of single nanoribbon of copper phthalocyanine

Copper phthalocyanine (CuPc) nanoribbon field-effect transistors were implemented as chemical sensors. They showed fast response and high reversibility in the detection of the tetrahydrofuran atmosphere at room temperature. The drain current of the field-effect transistor sensor decreased from 6.7 to 0.2 nA when the transistor was measured under the tetrahydrofuran atmosphere. The sensor was self-refreshable in a few minutes. These results demonstrate that the organic single crystalline nanoribbon transistors could effectively act as chemical sensors. Supported by the National Natural Science Foundation of China (Grant Nos. 20721061, 50725311, 60736004, 60771031), the Ministry of Science and Technology of China (Grant Nos. 2006CB806200, 2006CB932100), and Chinese Academy of Sciences     

A Water-Gated Organic Thin-Film Transistor for Glyphosate Detection: A Comparative Study with Fluorescence Sensing

This work reports the design of a highly sensitive solid-state sensor device based on a water-gated organic thin-film transistor (WG-OTFT) for the selective detection of herbicide glyphosate (GlyP) in water. A competitive assay among carboxylate-functionalized polythiophene, Cu²⁺, and GlyP was employed as a sensing mechanism. Molecular recognition phenomena and electrical double layer (EDL) (at the polymer/water interface) originated from the field-effect worked cooperatively to amplify the sensitivity for GlyP. The limit of detection of WG-OTFT (0.26 ppm) was lower than that of a fluorescence sensor chip (0.95 ppm) which is the conventional sensing method. In contrast to the previously reported insulated molecular wires to block interchain interactions, molecular aggregates under the field-effect has shown to be effective for amplification of sensitivity through “intra”- and “inter”-molecular wire effects. The opposite strategy in this study could pave the way for fully utilizing the sensing properties of polymer-based solid-state sensor devices.     

Chemical and biological sensors based on organic thin-film transistors

The application of organic thin-film transistors (OTFTs) to chemical and biological sensing is reviewed. This review covers transistors that are based on the modulation of current through thin organic semiconducting films, and includes both field-effect and electrochemical transistors. The advantages of using OTFTs as sensors (including high sensitivity and selectivity) are described, and results are presented for sensing analytes in both gaseous and aqueous environments. The primary emphasis is on the major developments in the field of OTFT sensing over the last 5–10 years, but some earlier work is discussed briefly to provide a foundation.     

Electronically monitoring biological interactions with carbon nanotube field-effect transistors

The year 2008 marks the 10th anniversary of the carbon nanotube field-effect transistor (NTFET). In the past decade a vast amount of effort has been placed on the development of NTFET based sensors for the detection of both chemical and biological species. Towards this end, NTFETs show great promise because of their extreme environmental sensitivity, small size, and ultra-low power requirements. Despite the great progress NTFETs have shown in the field of biological sensing, debate still exists over the mechanistic origins underlying the electronic response of NTFET devices, specifically whether analyte species interact with the carbon nanotube conduction channel or if interaction with the NTFET electrodes actually triggers device response. In this tutorial review, we describe the fabrication of NTFET devices, and detail several reports that illustrate recent advances in biological detection using NTFET devices, while highlighting the suggested mechanisms explaining the device response to analyte species. In doing this we hope to show that NTFET technology has the potential for low-cost and portable bioanalytical platforms.     

Analytical characteristics and sensitivity mechanisms of electrolyte-insulator-semiconductor system-based chemical sensors—a critical review

Recent trends in research and development of electrolyte-insulator-semiconductor (EIS) field-effect chemical sensors (ion-selective field-effect transistors, light-addressable potentiometric sensors, capacitive EIS-sensors) with inorganic gate insulators (oxide, nitride and chalcogenide films) are reviewed. Physical properties of EIS systems and basic mechanisms of their chemical sensitivity are examined. Analytical characteristics and sensing mechanisms of EIS pH sensors with oxide and nitride films, as well as metal ions sensors with chalcogenide films, are critically discussed. Prospects of future research on EIS field-effect biosensors are briefly outlined.